1. Field of the Invention
The present invention relates, in general, to clamps and, specifically, to clamps having a pivotal arm.
2. Description of the Art
Clamps are used in industrial applications to hold workpieces together at predetermined locations under force during work operations, such as machining, welding, etc. A typical fluid pressure actuated clamp utilizes a fluid-pressure actuated cylinder-piston fluid motor having a piston slidable within the cylinder housing by pressurized fluid. Movement of the piston extends and retracts a piston rod having an end extending outward from one end of the cylinder. The end of the piston rod is connected to a linkage to rotate a shaft carrying at least one pivotal clamp arm upon bi-directional rotation extension and retraction of the piston rod from a first open position to a second, workpiece engaging, closed position.
In high speed manufacturing production operations, it is necessary to know when the clamp arm is opened and/or closed before the next operation can be initiated. Electromechanical limit switches have been mounted at either or both of the open and closed positions of the clamp arm and mechanically engaged by the clamp arm to detect the open or closed position of the arm. Such switches are prone to breakage, misalignment, wear, etc.
Proximity switches have also been mounted at opposite ends of the fluid cylinder used to pivot the clamp arm to detect the piston position within the cylinder. Proximity switches thereby provide an indirect indication of the rotational position of the clamp arm by detecting whether the piston or piston rod is in the extended or retracted position equivalent to a closed or open position of the clamp arm.
However, the use of cylinder-operated proximity switches provides only an indirect indication of the position of the clamp arm. Damage to the clamp arm may render the clamp totally ineffective at clamping a workpiece; while the proximity switches still provide the indication of open or closed clamp arm position. In addition, if a workpiece is missing, misshaped or bent, the fluid cylinder will drive the clamp arm to the same closed position and the proximity switches will provide an indication of a fully closed clamp arm position. If the workpiece is out of position, the clamp arm which is moving under pressurized fluid force may encounter and deform a workpiece.
More importantly, the proximity switches, limit switches, etc., used to directly or indirectly detect the position of a clamp arm during movement between opened and closed positions do so only at the full open and full closed positions. In certain high speed assembly operations, this may delay the initiation of the next operation until the clamp arm reaches the fully opened or fully closed position; where the next initiating actions could actually have been started just prior to the movement of the clamp arm to the full open or full closed positions.
Thus, it would be desirable to provide a clamp arm position detector which determines the absolute position of a clamp arm during movement of the clamp arm between open and closed positions. It would also be desirable to provide a clamp arm position detector which is mountable on a standard clamp without significant modifications necessary to the clamp. It would also be desirable to provide a clamp arm position detector which is usable in left hand and right hand clamp applications without significant modification to the clamp. It would also be desirable to provide a clamp arm position detector which provides set points prior to full open and full closed clamp arm positions to be used to initiate the start of the next operation. It would also be desirable to provide a clamp arm position detector providing such set point wherein the set points are programmable over a set angular range of rotation of the clamp arm.